Growing Fuel, Fuelling Growth

Prof Diane HildebrandtDirector of MaPS Research Unit University of South Africa

Introduction to UNISA• UNISA is over 140 years old• UNISA is a mega University with over

400 000 students• UNISA was a forerunner of long distance

education• began to teach exclusively through

distance learning in 1946.

Introduction to MaPSMaPS stands for the Materials and Process

Synthesis Research UnitWe research in a number of areas:

Reactor design (Attainable Regions)Separation design (Column Profile Maps)Process Design for improved process

efficiencyFischer Tropsch

THE VISION

Our vision is to change the landscape by turning waste and other under-utilised resources into fuel, electricity and jobs

through strategic partnerships.

Our work is particularly aimed at Africa and the Developing World

The potential of waste:Globally it is estimated that we annually produce :

140 billion tons of biomass waste2 billions tons of municipal waste

From this we could produce 100 billions barrels of green synthetic crude oilUsing gasification followed by Fischer Tropsch

The world currently consumes around 34 billion barrels of oil annually.

A Chemical Process: How do we reduce CO2 emissions

6

• Why do processes emit CO2﹖• How much CO2 does a process need to emit﹖• How do we determine this﹖

Chemical ProcessFeeds Products

CO2Must include utilities

Process Design: a New Approach

We look at the process macroscopically We identify the process inputs that give rise

to the desired products as well as the by-products also including utilities

Looking at a process macroscopically allows one to determine targets

A target represents the best possible performance for a process

The performance of real processes can be compared to the target to determine opportunities for improvement.

We can compare different processes (options) using their targets

7

Process Design: The Science

There are 3 tools that we use to synthesise and analyse processes: Mass BalanceEnergy Balance Entropy/Work Balance

Each of these tools can be used to determine the target performance of a process

8

Mass BalanceSets the overall

extents across the process, equipment

or reactions

Energy balanceSets the heat load over the process,

equipment or reactions

Entropy/ Gibbs Balance

Sets the work load across the process,

equipment or reactions

Will focus on G and H in this

talk

Chemical Process

Feeds Products

The Process Work and Energy Balance

• The amount of heat Q that must be supplied is: Q=∆Hprocess

The amount of work W that needs to be supplied is:W ≥ ∆Gprocess

10

Inputs

OutputsProcess

Q

W

Result 1A process, equipment or reaction can be represented as a vector on the GH Plot

Example: CTL

3/2C+ H2O = -CH2- +1/2CO2

ΔHprocess = 58 kJ/mol CH2

ΔGprocess = 41 kJ/mol CH2

-100 -80 -60 -40 -20 0 20 40 60 80 100

H [kJ/mol]

-100

-80

-60

-40

-20

0

20

40

60

80

100

G [k

J/m

ol]

149

179

211

249

298

372

509

899

+/--600-211-7404987119149

Work to be added = Δ Gprocess

Heat to be added = Δ Hprocess

• Putting heat in is relatively easy• But how do we put work in?

Result 2Sequencing of Processes can be represented by vector operations

CTL

Gasification FT Synthesis

CO+2 H2

• Gasification 3/2C+ 2H2O =CO + 2H2 + 1/2CO2

• FT reactionCO+2H2 = -CH2- +H2O

Overall: 3/2C+ H2O = -CH2- +1/2CO2

-100 -80 -60 -40 -20 0 20 40 60 80 100

H [kJ/mol]

-100

-80

-60

-40

-20

0

20

40

60

80

100

G [k

J/m

ol]

149

179

211

249

298

372

509

899

+/--600-211-7404987119149

NOT TO SCALE

3/2C+ 2H2O =CO + 2H2 + 1/2CO2

CO+2H2 = -CH2- +H2O

3/2C+ H2O = -CH2- +1/2CO2

Processes to Vectors:

Process 1

Process 2

A B

A

B

1 2Processes in Parallel

Process

Larger Process

Scaling of process

Result 3:The reversible operating temperatures can be deduced from GH plot

How do we add the work to a Process?

The major way we have of supplying work to a process is by setting the temperature of the heat that is added to the process.

Can use P-V work to a lesser extent egmethanol and ammonia processes

For a reversible work addition process, there is a temperature that we call the Carnot temperature TCarnot where:W= ∆Gprocess= ∆Hprocess(1-To/TCarnot)

19

The Process Work Balance At the Carnot temperature TCarnot, the heat carries

the required amount of work into the process

20

∆GprocessWork

required by process

WcarnotVirtual work carried in by

heat

CO2Process

C

H2O CH2

Q

W

-100 -80 -60 -40 -20 0 20 40 60 80 100

H [kJ/mol]

-100

-80

-60

-40

-20

0

20

40

60

80

100

G [k

J/m

ol]

149

179

211

249

298

372

509

899

+/--600-211-7404987119149

Tc = 800 K

Tc = 370 K

All points along this line have the same Tcarnot = 800 K

If heat is added at TCarnot, the process will be reversible

All points along this line have the same Tcarnot = 370 K

Adding or rejecting heat at 370 K will make process lying on this line reversible

Result 4If work cannot be put in by heat at a single suitable temperature, then work can be put into Processes using the process as a heat engine

-100 -80 -60 -40 -20 0 20 40 60 80 100

H [kJ/mol]

-100

-80

-60

-40

-20

0

20

40

60

80

100

G [k

J/m

ol]

149

179

211

249

298

372

509

899

+/--600-211-7404987119149

Heat in at high temperature carries work in with it

Reject heat at low temperature which carries work out with it.

Gasification:1500 K

FT Synthesis:500 K and 30 bar

Not To Scale

Result 5Degree of reversibility can be seen on GH plot

-100 -80 -60 -40 -20 0 20 40 60 80 100

H [kJ/mol]

-100

-80

-60

-40

-20

0

20

40

60

80

100

G [k

J/m

ol]

149

179

211

249

298

372

509

899

+/--600-211-7404987119149

Tc = 800 K

T < Tcarnot

T>Tcarnot

Work deficient

Excess Work Added

• W deficient• Additional W will need to

be added• Compression?

Excess work added lost as irreversibility

Result 6In order to design a process with a high degree of reversibilityneed to target the origin of the GH plot

G

H

• ExampleSteam Reforming:Wish to produce CO: H2 = 1:2Reduce CO2 emissions

Overall G-H Plot making a 2:1 ratio syngas from methane

∆G

∆ H Combustion

WGS

Reform

Phase

Process

2:1 Processes

G-H diagram

224 H3OCOHCH +→+

OH2COO2CH 2224 +→+

OHCOHCO 222 +↔+

)g(OH)l(OH 22 →

Target overall mass balance

Flow sheet formulation: Steam Reforming

0,00

20,00

40,00

60,00

80,00

100,00

120,00

0,00 50,00 100,00 150,00 200,00

G

H

Reforming

CH4

H2O

CO H2SteamReforming

-20,00

0,00

20,00

40,00

60,00

80,00

100,00

120,00

-40,00 -20,00 0,00 20,00 40,00 60,00 80,00 100,00 120,00 140,00 160,00 180,00

G

H

CH4

H2OCO H2

O2

H2OCO2

SteamReforming

Combustion

-12

-10

-8

-6

-4

-2

0-16 -14 -12 -10 -8 -6 -4 -2 0

G

H

CH4

H2OCO H2

O2

H2OCO2

CO 2H2

H2O

Combustion

SteamReforming

Water Gas Shift

-3

-2,5

-2

-1,5

-1

-0,5

0-4 -3,5 -3 -2,5 -2 -1,5 -1 -0,5 0

G

H

CH4

H2OCO H2

O2

H2OCO2CO 2H2

H2O

CO 2H2

H2OSteam

Reforming

Combustion

Water Gas Shift

Sep

ara

tion

-1,8

-1,6

-1,4

-1,2

-1

-0,8

-0,6

-0,4

-0,2

0-4 -3,5 -3 -2,5 -2 -1,5 -1 -0,5 0

G

H

CH4

H2OCO H2

O2

H2OCO2CO 2H2

H2O

CO 2H2

H2OH2OSteam

Reforming

Combustion

Water Gas Shift

Sep

ara

tion

Phase Change

-0,9

-0,8

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,1

0-1 -0,5 0 0,5 1

G

H

CH4

H2OCO H2

O2

H2OCO2CO 2H2

H2O

CO2H2

H2OH2OSteam

Reforming

Combustion

Water Gas Shift

Reformer1273K34atm

WGS974K

34atmSep

Meth387K1atm

1.21 CH4

0.42 O2

0.24 H2O

1.42 H2O1CO3H20.21CO2

1.76 H2O

1.76 H2O0.88 CO2

2.66 H21.33 CO

0.88 CO2

1 CO2

0.12 CO2

2.66 H21.33 CO 1.33 CH3OH

Carbon Negative Methanol Production

Waste to Energy:

Waste to Energy38

Chemical ProcessFeeds Products

These could be:• Garbage• Agricultural waste• Crops grown for

energy (bamboo, grasses etc)

• Liquid fuels• Electricity• Heating• Chemicals…

..

Constraints: Waste to Energy39

Chemical Process

• Scale of the plant has to match size of resource

• Capital costs have to match funding resources

• Bigger is not better!

Complexity of the plant has to match the application• Unskilled operators?• Difficulty maintaining

equipment?

Challenge:

How can we make small processes that convert waste and biomass to fuel, electricity, heat and which are:

• Socially acceptable• Environmentally friendly• Efficient

• Cheap• Simple• Robust

Theory Social

Technology

CommunitySocial ScientistEngineersGovernment

Application to small scale processes Use techniques to identify

Sources of efficiency (co produce electricity and heat) Sources of inefficiencies (no air sep, no cryogenic

separation, no recycles, gasification temperature low, …)

With biomass feeds, want to return P,K and N if possible back to soil where crop originated from.

Need low cost FT catalyst that can be reduced with syngas at reaction conditions, have long life, can be regenerated….

Keep equipment simple (down draft gasifiers, gas engines, shell and tube FT reactors, corn cobbs for filters,….)

Summary

We have shown that we have developed a way to synthesise processes

Lower efficiency effectively means increased carbon dioxide emissions

The method is based on thermodynamics, and in particular G and H

With minimal information about the details of the plant it enables us to synthesise a process and determine targets.

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Conclusion A process, equipment or reaction can

be represented as a vector in GH space The diagram is 2 dimensional and

remains 2 dimensional no matter how complex the process

Vector maths can be used to synthesize processes

Very powerful yet very simple approach which has the potential to synthesize more efficient processes with reduced GHG emissions

Acknowledgements

Acknowledgements (in no particular order)

David Glasser

James Fox

Celestin Sempuga

All the students and colleagues who have worked on this.

Thank YouDiane.hildebrandt@outlook.com